OK, so let's test the science advocates out here.............

by NotaNess 40 Replies latest watchtower bible

  • NotaNess

    I'll start it off, then someone else give them a different challenge if you can think of any.

    Please give definitive examples that by evolution, a species has changed into something else. Give two separate findings by scientists, and it can't include any comments like "so we believe", "so we conclude that", or "the evidence shows that there could have been".....the WTS has those copyrighted.

    Try and give un-doctored photographic proof, where possible, etc. By the way the hominid skulls and the like will not be accepted, transition has never been proven, I don't think, just that they are different, and scientists "believe", they are pre-homo-sapiens.

    I'm not saying you won't have examples, we just want you to walk the talk. Support your claims. You're so sure of the science and evolution. Now bring it.

  • Shazard

    More simple question is. How much qunatitativ information can be produced by evolutionary prcoess. Calculations, evidence, demonstrations?

  • 5go

    I shall work on that if you can do one thing.

    Prove God can or can not, heat a burrito so hot that even he can not eat.

  • Arthur
    Please give definitive examples that by evolution, a species has changed into something else. Give two separate findings by scientists, and it can't include any comments like "so we believe", "so we conclude that", or "the evidence shows that there could have been"....

    I would tend to think that when scientists use cautionary language such as "the evidence shows", it reveals an intellectual honesty that is absent in dogmatic assertions. It seem that when any scientist comes out and asserts that they have undeniable "proof" of something, you get fiascos like the Piltdown Man.

  • 5go
    Try and give un-doctored photographic proof, where possible, etc. By the way the hominid skulls and the like will not be accepted, transition has never been proven, I don't think, just that they are different, and scientists "believe", they are pre-homo-sapiens.

    The highlighted statement is like me asking you for a picture of god so as the prove he exist.

    By the way I need a picture of god as well.

  • 5go



    From Wikipedia, the free encyclopedia

    Jump to: navigation, search <area href="/wiki/Wikipedia:Protection_policy" alt="This page has been semi-protected from editing" shape="RECT" title="This page has been semi-protected from editing" coords="0,0,156,156">alt This article is about evolution in biology. For other uses, see Evolution (disambiguation).
    For a non-technical introduction to the topic, please see Introduction to evolution. An inherited trait becoming more common is evolution. alt An inherited trait becoming more common is evolution.

    In biology, evolution is the change in a population's inheritedtraits from generation to generation. These traits are the expression of genes that are copied and passed on to offspring during reproduction. Mutations and other random changes in these genes can produce new or altered traits, resulting in heritable differences (genetic variation) between organisms. New traits can also come from transfer of genes between populations, as in horizontal gene transfer or breeding between species. Evolution occurs when these differences become more common or rare in a population, either randomly through genetic drift or nonrandomly through natural selection.

    Natural selection causes inheritable traits that are helpful for survival and reproduction to become more common and harmful traits to become more rare. This occurs because organisms with these advantageous traits produce more offspring, thus passing more copies of the traits on to the next generation. [1] [2] [3] Over very long periods of time, adaptations are produced by a combination of the continuous production of small, random changes in traits, followed by natural selection of the variants best-suited for their environment. [4]

    A species is a group of animals that can breed with one another. However, when a species is separated into different populations that are prevented from reproducing with each other, random mutation and drift, combined with different environments selecting for and against different traits, results in these populations accumulating differences over time and eventually becoming two separate new species. The similarities between all organisms suggest that all known species are descended from a single ancestral species through this process of gradual divergence. [1] [5] [6]

    The theory of evolution by natural selection was first proposed by Charles Darwin and Alfred Russel Wallace and put forth in detail in Darwin's 1859 book On the Origin of Species. In the 1930s, Darwinian natural selection was combined with Mendelianinheritance to form the modern evolutionary synthesis. [4] With its enormous explanatory and predictive power, this theory has become the central organizing principle of modern biology, providing a unifying explanation for the diversity of life on Earth. [7] [8] [9]

    Part of the Biology series on
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    History of evolutionary thought

    For more details on this topic, see History of evolutionary thought.
    Charles Darwin at age 51, just after publishing The Origin of Species. alt Charles Darwin at age 51, just after publishing The Origin of Species. Gregor Mendel's work on the inheritance of traits in pea plants laid the foundation for genetics. alt Gregor Mendel's work on the inheritance of traits in pea plants laid the foundation for genetics.

    Evolutionary ideas such as common descent and the transmutation of species have existed since at least the 6th century BC, when they were expounded by the Greek philosopher Anaximander. [10] As biological knowledge grew in the 18th century, a variety of such ideas developed, beginning with Pierre Maupertuis in 1745. [11]

    The first convincing exposition of a mechanism by which evolutionary change could occur was not made until 1858, when Charles Darwin and Alfred Russel Wallace jointly proposed the theory of evolution by natural selection to the Linnean Society of London in separate papers. [12] Shortly after, Darwin's publication of The Origin of Species provided detailed support for the theory and led to increasingly wide acceptance of the occurrence of evolution. However, Darwin's specific ideas about evolution, such as gradualism and natural selection, were strongly contested at first. Lamarckists argued that transmutation of species occurred as parents passed on adaptations acquired during their lifetimes. [13] Eventually, when experiments failed to support it, this popular rival theory was abandoned in favor of Darwinism. [14]

    However, Darwin could not account for how traits were passed down from generation to generation. A mechanism was provided in 1865 by Gregor Mendel, whose research revealed that distinct traits were inherited in a well-defined and predictable manner. [15] When Mendel's work was rediscovered in 1900, disagreements over the rate of evolution predicted by early geneticists and biometricians led to a rift between the Mendelian and Darwinian models of evolution. This contradiction was reconciled in the 1930s through the work of biologists such as Ronald Fisher. The end result was a combination of Darwinian natural selection with Mendelian inheritance, the modern evolutionary synthesis, or "Neo-Darwinism". [16]

    In the 1940s, the identification of DNA as the genetic material by Oswald Avery and colleagues, [17] and the subsequent publication of the structure of DNA by James Watson and Francis Crick in 1953, [18] demonstrated the physical basis for inheritance. Since then, genetics and molecular biology have become increasingly important in evolutionary biology. [19]


    DNA structure, bases are in the center, surrounded by phosphate - sugar chains in a double helix. alt DNA structure, bases are in the center, surrounded by phosphate - sugar chains in a double helix. [20]

    For more details on this topic, see Introduction to genetics, Genetics, and Heredity.

    Inheritance in organisms occurs through discrete traits, which are one particular characteristic of the organism. In humans for example, eye color is an inherited character and a person could inherit the trait of having brown eyes from one of their parents. [21] Inherited traits are controlled by genes and the set of genes within an organism is called its genotype. [22] Most hereditary traits are inherited through Mendelian inheritance, where offspring have the trait of either one or the other of their parents, but not a mixture of the two traits.

    The complete set of observable traits of an organism, its phenotype, comes from the interaction of its genotype with the environment. [23] As a result, not every aspect of an organism's phenotype is inherited. For example, the characteristic of a person having a suntanned skin is the result of the interaction between their genotype and sunlight, and a suntan is not hereditary. However, people differ in their genotype and thus have different responses to sunlight; the most striking examples being people with the inherited trait of albinism, who do not tan at all and are therefore highly sensitive to sunburn. [24]

    Genes are the physical basis of inherited traits and are defined as regions within DNA molecules. [22] DNA is made of a backbone of alternating sugars and phosphate groups, attached to each sugar is one of four types of molecules called bases. Genes are distinguished by their differing sequences of bases; these sequences encode the genetic information. This information is read using the genetic code; a gene's DNA sequence specifies a corresponding sequence of the amino acids within a protein. When genes are used by an organism, the DNA is transcribed into RNA and then this RNA is translated into protein. Within cells, the long strands of DNA associate with proteins to form structures called chromosomes. A specific location within the DNA in a chromosome is known as a locus, with a variant of a DNA sequence at a given locus called an allele. These DNA sequences can change through mutations, producing new alleles. If these mutations happen within a gene, they may affect the traits that the genes control and alter the phenotype of the organism. This simple correspondence between a mutation and a trait works in many cases, although complex traits such as disease resistance are controlled by multiple interacting genes. [25] [26]

    Changes in genes can also influence traits through DNA modifications such as DNA methylation; such modifications do not change the sequence of the DNA in a gene, but cause an inherited change in the use of that gene. [27] Non-DNA based forms of heritable variation exist, such as transmission of the secondary structures of prions in yeast. [28] However, it is not known if these mechanisms produce specific heritable changes in response to the environment. If this does occur, then some instances of evolution would be separate from standard genetic inheritance. [29] However, such processes are rare and often reversible, and their significance to evolution remains unclear. [30]


    For more details on this topic, see Genetic variation and Population genetics.

    An individual's phenotype results from the interaction of their genotype with the environment. [26] Thus, the variation in phenotypes within a population reflects the variation in this population's genotypes. The modern evolutionary synthesis defines evolution as the change over time in the relative frequencies of alleles in a population. [31] The frequency of these variants may fluctuate in the population, becoming more or less prevalent relative to other alleles of that gene. All evolutionary forces act by driving these changes in allele frequency in one direction or another. Variation disappears when an allele reaches the point of fixation — when it either disappears from the population, or when it replaces the ancestral allele entirely. [32]

    Variation comes from mutations in genetic material, migration between populations (gene flow), and the reshuffling of genes during sexual reproduction. In some organisms, variation is also produced by the mixing of genetic material between different species through horizontal gene transfer in bacteria, and hybridization in plants. [33] [34] Despite all the processes that introduce variation, most sites in the genome of a species are identical in all individuals of this species. [35] However, even relatively small changes in genotype can lead to dramatic changes in phenotype, with chimpanzees and humans only differing in about 5% of their genomes. [36]


    For more details on this topic, see Mutation.

    Genetic variation arises due to random mutations that occur in the genomes of all organisms. Mutations are transmissible changes in genetic material, and are often caused by external factors such as radiation and mutagenic chemicals, as well as errors that occur during meiosis or DNA replication. [37] Viruses and mobile DNA sequences such as transposons, are another cause of mutations. [38] [39] Individual genes can be affected by two different types of mutations. In point mutations, a single base pair is altered. This change in a single base pair may or may not affect the function of the gene. The other type of mutations are the deletion and insertion of base pairs. These changes often cause a loss of the gene's function, as they cause a shift in reading frame and thus change many amino acid codons simultaneously. [40]

    Chromosomes from a person with Werner syndrome. Each chromosome is labeled with a different color. The gold-tipped maroon staining shows fused DNA from two chromosomes. alt Chromosomes from a person with Werner syndrome. Each chromosome is labeled with a different color. The gold-tipped maroon staining shows fused DNA from two chromosomes.

    In multicellular organisms, mutations can be classified into germline mutations that occur in the gametes and thus can be passed onto offspring, and somatic mutations that can trigger cell death, or cause cancer. [37] These somatic mutations are not inherited and therefore have no effect on evolutionary processes. Due to the damaging effects that mutations can have on cells, organisms have evolved multiple mechanisms such as DNA repair that reduce mutation rates. However, the optimal mutation rate for an organism is a trade-off between short-term costs, such as the energy expended on DNA repair and the effects of deleterious mutations, and the long-term benefits of advantageous mutations. [41] Organisms such as bacteria can even increase their mutation rate in response to stress, leading to the evolution of novel alleles that counter the source of stress. [42]

    Most genes belong to larger families of genes that are derived though mutation from one or more ancestral genes. [43] Novel genes can be produced either through duplication and mutation of an ancestral gene, or the recombination of protein domains to form a new combination of these structural modules. [44] [45] Gene duplications, which may occur through a number of mechanisms, are believed to be one major source of raw material for evolving new genes, as tens to hundreds of genes are duplicated in animal genomes every million years. [46] At a higher level, the duplication of entire genomes to produce polyploid organisms also appears to have been important in evolution, particularly in vertebrates and in plants. [47] Another possible advantage of gene duplication is that overlapping or redundant function in families of genes can allow retention of alleles that would otherwise have deleterious effects, thus increasing genetic diversity. [48]

    Changes in chromosome number may also involve the breakage and rearrangement of genes in chromosomes. Large chromosomal rearrangements do not necessarily change gene function, but can result in reproductive isolation. [49] An example of chromosomal rearrangements is the fusion of two chromosomes in the Homo genus that produced human chromosome 2; this fusion did not occur in the chimpanzeelineage, and chimpanzees retain two separate chromosomes. [50] However, chromosomal rearrangements do not appear to have driven the divergence of the human and chimpanzee lineages. [51] The major role of such chromosomal rearrangements in speciation may be to reduce recombination, thus preventing separation of linked alleles and accelerating divergence. [52]


    For more details on this topic, see Genetic recombination and Sexual reproduction.

    In asexual organisms, genes will be inherited together, they are linked, as they have no opportunity to mix with genes from other organisms during reproduction. However, the offspring of sexual organisms contain a random mixture of their parents' chromosomes, which is the result of a process called independent assortment. Sexual organisms can also exchange DNA between two matching chromosomes in a process called genetic recombination. [53] This shuffling of genetic material between chromosomes allows even alleles of genes that are close together in the genome to be inherited independently. However, the recombination rate is not very high and in humans is approximately one recombination event per 1,000,000 base pairs. [54] Therefore, alleles close together on a chromosome are not often shuffled away from each other, but tend to be inherited together. This tendency is measured by comparing the co-occurrence of two alleles, their linkage disequilibrium. A set of alleles that are often inherited together is called a haplotype and this co-inheritance can indicate that the locus is under positive selection (see below). [55]

    Recombination in sexual organisms allows disadvantageous mutations to be purged and beneficial mutations to be retained more efficiently than in asexual organisms. [56] In addition, recombination can lead to more individuals with new and advantageous gene combinations being produced. These benefits can be identified by looking at the effects of situations where alleles cannot be separated by recombination, such as in mammalian Y chromosomes. [57] In these circumstances, there is a reduction in effective population size called the Hill-Robertson effect, [58] which causes the accumulation of deleterious mutations. [59] These positive effects of recombination are balanced by the facts that it can cause mutations (as it involves the breaking and rejoining of the DNA strands) and it can also separate gene combinations that have been successful in previous generations. [56] The optimal rate of recombination for a species is therefore a trade-off between these conflicting factors.

    Mechanisms of evolution

    There are many basic mechanisms of evolutionary change: natural selection, genetic drift, and others like gene flow from migration. Gene flow is the transfer of genetic material within and between populations, genetic drift is the random sampling of a generation's genes during reproduction, which causes random changes in the frequency of alleles, and natural selection is the non-random propagation of genes that favor survival and reproduction. The relative importance of these three forces in driving evolution is variable. The importance of natural selection and genetic drift depends on the effective population size, which is the number of organisms capable of breeding, as well as the strength of selection. [60] Natural selection probably predominates in large populations, while genetic drift dominates in small populations. As a result, changing population size can dramatically influence the course of evolution. Population bottlenecks, where the population shrinks in size temporarily to a small number of individuals and therefore loses much genetic variation, result in a more uniform population and the loss of most rare variation. [32] Bottlenecks may also result from alterations in gene flow such as decreased migration, founder effects, or population subdivision. [60]

    Natural selection

    Natural selection of a population for dark coloration. alt Natural selection of a population for dark coloration.

    For more details on this topic, see Natural selection and Fitness (biology).

    Natural selection results from the difference in reproductive success between individuals in a population and causes adaptation. [61] It has often been called a "self-evident" mechanism because it necessarily follows from the following facts:

    • Natural, heritable variation exists within populations and among species
    • Organisms are superfecund (produce more offspring than can possibly survive)
    • Organisms in a population vary in their ability to survive and reproduce
    • In any generation, successful reproducers pass their heritable traits to the next generation, while unsuccessful reproducers do not.

    The central concept of natural selection is the evolutionary fitness of an organism. This is a measure of the organism's genetic contribution to the next generation. However, this is not the same as the total number of the organism's offspring: instead fitness measures the proportion of subsequent generations that carry the organism's genes. [62] Consequently, if an allele produces a trait that increases fitness, with each generation this allele will become more common within a population. Examples of traits that can increase fitness are enhanced survival, and increased fecundity. Conversely, a decrease in fitness caused by a deleterious allele results in this allele becoming rarer. [1] [2] Importantly, the fitness of an allele is not a fixed characteristic, if the environment changes, previously neutral and harmful traits may become beneficial and previously beneficial traits become deleterious.

    Natural selection within a population can be subcategorized into three different modes: directional selection (a shift in the mean trait value over time); [63] disruptive selection (selection for extreme trait values on both ends, or "tails" of the distribution, often resulting in a bimodal distribution and selection against the mean); and stabilizing selection (also called purifying selection — selection against extreme trait values on both ends, and a decrease in variance around the mean.) [64]

    A special case of natural selection is sexual selection: selection for any trait whose presence is directly correlated with mating success due to preferential mate choice. [65] Traits that evolved via sexual selection are particularly prominent among males of animal species. Despite the fact that such traits may decrease the survival of individual males (e.g. cumbersome antlers, mating calls or bright colors that attract predators, male-male fighting over access to mates), [66] reproductive success is usually higher in males that show hard to fake, sexually selected traits. [67]

    An active area of current research is the level of selection, with natural selection being proposed to work at the level of genes, cells, individual organisms, groups of organisms and even species. [68] None of these models are mutually-exclusive and selection may act on multiple levels simultaneously. [69] In the gene-centered view of evolution, which is the lowest level of selection, intragenomic conflict is caused by "replicators" such as transposons that can multiply within genomes, [70] while group selection may allow the evolution of co-operation, as discussed below. [71]

    Simulations of genetic drift of 20 alleles in populations of 10 (top) and 100 (bottom). Alleles drift to fixation more rapidly in the smaller population. alt Simulations of genetic drift of 20 alleles in populations of 10 (top) and 100 (bottom). Alleles drift to fixation more rapidly in the smaller population.

    Genetic drift

    For more details on this topic, see Genetic drift and Effective population size.

    Genetic drift is the change in allele frequency from one generation to the next that occurs because alleles in the offspring generation are a random sample of alleles in the parent generation, and are thus subject to sampling error. [32] As a result, in the absence of selection on the alleles, allele frequencies tend to "drift" upward or downward in a random walk, until they eventually become fixed - that is, going to 0% or 100% frequency. The time for an allele to become fixed in the population by genetic drift (that is, for all individuals in the population to carry that allele) depends on population size, with smaller populations requiring a shorter time for fixation. [72] Fluctuations in allele frequency between generations may therefore eliminate some alleles from a population due to chance alone. Two separate populations that began with the same allele frequencies can therefore drift apart by random fluctuation into two divergent populations with different sets of alleles. [73]

    Although natural selection is responsible for adaptation, the relative importance of the two forces of natural selection and genetic drift in driving evolutionary change in general is an area of current research in evolutionary biology. [74] These investigations were prompted by the neutral theory of molecular evolution, which proposed that most evolutionary changes in organisms are the result the fixation of neutral mutations that do not affect the fitness of an organism. [75] Hence, in this model, most genetic changes in a population are the result of constant mutation pressure and random genetic drift. [76] [77]

    Gene flow

    For more details on this topic, see Gene flow, Hybrid, and Horizontal gene transfer.
    Map showing distribution of camelids since their origin in North America in the pleistocene epoch. alt Map showing distribution of camelids since their origin in North America in the pleistocene epoch.

    Gene flow is the exchange of genes between populations, most commonly of the same species. [78] Examples of gene flow within a species include the migration and then breeding of organisms, or the exchange of pollen. Gene transfer between species includes the formation of hybrid organisms and horizontal gene transfer.

    Migration into or out of a population can change allele frequencies. Immigration may add new genetic material to the established gene pool of a population. Conversely, emigration may remove genetic material. As reproductive isolation is required for speciation, gene flow may delay speciation by homogenizing two diverging populations. Gene flow is hindered by mountain ranges, oceans and deserts or even man-made structures such as the Great Wall of China, which has hindered the flow of plant genes. [79]

    Depending on how far two species have diverged since their last common ancestor, it may still be possible for them to produce viable offspring, as with horses and donkeys mating to produce mules. [80] Such hybrids are generally infertile, due to mispairings of chromosomes during meiosis. In this case, closely-related species may regularly interbreed, but hybrids will be selected against and the populations will remain distinct. However, viable hybrids can also be formed and these new species can either have properties intermediate between their parent species, or a radically different phenotype. [81] Hybridization rarely leads to new species in animals, although this has been seen in the tree frog Hyla versicolor. [82] Hybridization is however an important means of speciation in plants, since polyploidy (having more than two copies of each chromosome) is tolerated in plants more readily than in animals. [47] Polyploidy is important in hybrids as it allows reproduction, with the two different sets of chromosomes each being able to pair with an identical partner during meiosis. [83] Polypolids also have more genetic diversity, which allows them to resist the effects of inbreeding. [84]

    Horizontal gene transfer is the transfer of genetic material from one organism to another organism that is not its offspring. Horizontal gene transfer is common among bacteria, even between very distantly-related species. [85] In medicine, this contributes to the spread of antibiotic resistance, as when one bacteria acquires resistance genes it can transfer them to many other species. [86] Horizontal transfer of genes from bacteria to eukaryotes such as the yeast Saccharomyces cerevisiae and the adzuki bean beetle Callosobruchus chinensis may also have occurred. [87] [88] Viruses can also carry DNA between organisms, allowing transfer of genes even across biological domains. [89]

    Horizontal gene transfer has also occurred within eukaryotes, from their chloroplast and mitochondrial genome to their nuclear genome. [90] According to endosymbiotic theory, chloroplasts and mitochondria probably originated as bacterial endosymbionts of a progenitor to the eukaryotic cell. [91] Horizontal gene transfer complicates phylogenetics, since it produces genetic connections between distantly-related species. [92]

    Outcomes of evolution

    For more details on this topic, see Macroevolution and Microevolution.

    The outcomes of evolution are generally divided into macroevolution, which is evolution that occurs at or above the level of species and microevolution, which refers to smaller evolutionary changes (typically described as changes in allele frequencies) within a species or population. Within the modern evolutionary synthesis, in most cases macroevolution is thought of as the compounded effects of microevolution. [93] Thus, the distinction between micro- and macroevolution is not a fundamental one - the major difference between them is simply of the time involved. [94] However, in some cases speciation events may involve the rapid development of genuinely novel characteristics, such as hybrid genomes and changes in development, and here micro- and macroevolution can be distinct. [95]


    For more details on this topic, see Adaptation.

    As a result of natural selection, organisms undergo adaptation, which is the gradual accumulation of new traits that cause a population of organisms to become better suited to surviving and reproducing in their particular environment. [61] Adaptations are defined traits that not only enhance a specific function, but also evolved to perform that function. [96] These adaptations are the result of gradual modifications of existing traits and this adaptation process can cause either the gain of a new feature or the loss of an ancestral feature. Bacterial adaptation to antibiotic selection shows both these types of adaptation, with mutations causing antibiotic resistance either by modifying the target of the drug, or causing the loss of the transporters that allow the drug into the cell. [97]

    However, many traits that appear to be adaptations are in fact exaptations that originally had one function, but were later co-opted for something else. [98] For example, the forelimbs of penguins were wings before they evolved into flippers. [99] Additionally, adaptation has no objective or absolute value: a trait that increases fitness in one environment may decrease it in another. As an example, light pigmentation is an advantageous adaptation for camouflage in light-colored habitats, but disadvantageous in dark-colored environments. [100]

    A baleen whale skeleton. Letters a and b label the flipper bones, which were adapted from the front leg bones of the whale's terrestrial ancestors: while c indicates the vestigial remnants of the hind legs. alt A baleen whale skeleton. Letters a and b label the flipper bones, which were adapted from the front leg bones of the whale's terrestrial ancestors: while c indicates the vestigial remnants of the hind legs.

    As adaptation occurs through the gradual modification of existing structures, structures with similar internal organization may have very different functions in related organisms. This is the result of a single ancestral structure being adapted to function in different ways. Vertebrate limbs are a common example of such homologous structures. The bones within bat wings, for example, are structurally similar to both human hands and seal flippers, due to the common descent of these structures from an ancestor that also had 5 digits at the end of each forelimb. Other idiosyncratic anatomical features, such as the panda's "thumb", indicate that an organism's evolutionary lineage can limit what adaptions are possible. [101]

    During adaption, some structures may lose their original function and become vestigial structures. [102] Such structures may have little or no function in a current species, yet have a clear function in ancestral species, or other closely-related species. Examples include the non-functional remains of eyes in blind cave-dwelling fish, [103] wings in flightless birds, [104] and the presence of hip bones in whales and snakes. [105] Examples of vestigial structures in humans include wisdom teeth, [106] the coccyx, [102] and the vermiform appendix. [107]

    An area of current investigation in evolutionary developmental biology is the developmental basis of adaptations. [108] This research addresses the origin and evolution of embryonic development; how modifications of development and developmental processes produce novel features, and the role of developmental plasticity in evolution. [109] [110] These studies have shown that evolution can alter developmental processes to create new structures, such as embryonic bone structures that develop into the jaw in other animals instead forming the ossicles of the middle ear in mammals. [111] It is also possible for structures that have been lost in evolution to reappear due to changes in developmental genes, such as a mutation in chickens causing embryos to grow teeth similar to those of crocodiles. [112] In addition, developmental programs can be conserved in extremely diverse organisms, such as eye development genes that are common to jellyfish, insects, and mammals. [113]


    For more details on this topic, see Complexity and Complex adaptive system.
    Passive versus active trends in the evolution of complexity. Organisms at the beginning of the processes are colored red. Numbers of organisms are shown by the height of the bars, with the graphs moving up in a time series. alt Passive versus active trends in the evolution of complexity. Organisms at the beginning of the processes are colored red. Numbers of organisms are shown by the height of the bars, with the graphs moving up in a time series.

    Evolution has produced some remarkably complex organisms, but this feature is hard to measure in biology, with properties such as gene content, the number of cell types or morphology all being used to assess an organism's complexity. [114] The observation that complex organisms can be produced from simpler ones has led to the common idea of evolution being progressive and leading towards what are viewed as "higher organisms". [115] If this were generally true, evolution would possess an active trend towards complexity. As shown to the right, in this type of process the value of the most common amount of complexity would increase over time. [116] Indeed, some computer models have suggested that the generation of complex organisms is an inescapable feature of evolution. [117] [118]

    However, the idea of a general trend towards complexity in evolution can also be explained through a passive process. [116] This involves an increase in variance but the most common value does not change. Thus, the maximum level of complexity increases over time, but only as an indirect product of there being more organisms in total. In this hypothesis, the apparent trend towards complex organisms is an illusion resulting from concentrating on the small number of large, complex organisms that inhabit the right-hand tail of the complexity distribution and ignoring simpler and much more common organisms. This passive model emphasises that the overwhelming majority of species are microscopicprokaryotes, [119] which comprise about half the world's biomass. [120] constitute the vast majority of Earth's biodiversity. [121] Consequently, microscopic life dominates Earth, and large organisms only appear more diverse due to sampling bias.

    Co-evolution and cooperation

    For more details on this topic, see Co-evolution, Reciprocity (evolution), and Altruism in animals.

    A major part of the environment of living organisms are other organisms, such as predators, prey or their siblings. Interactions between organisms can produce both conflict and co-operation. When the interaction is between species, the evolution of one species can exert a selective pressure on a second species. This second species can then adapt and, in turn, exert a new selective pressure on the first species. This mutually-reinforcing selection produces co-evolution. [122] In co-evolution, pairs of organisms such as mutualists, a pathogen and a host, or a predator and its prey undergo matched adaptations. An example is the production of tetrodotoxin in the rough-skinned newt and the co-evolution of the common garter snake. The co-evolution between this predator-prey pair is an example of an evolutionary arms race and has produced very high levels of toxin in the newt and correspondingly high levels of toxin resistance in the snake. [123] [124] Extreme co-evolutionary adaptations also occur between plants and their mutualist mycorrhizal fungi; here the fungi actually grow inside plant cells and exchange nutrients with their hosts, while sending signals that suppress the plant immune system. [125] [126]

    However, not all interactions involve conflict. One of the most striking features of the natural world is that genes, cells, and organisms cooperate to form higher-order entities. For example, cells in animals sacrifice their reproduction to increase the fitness of the entire organism. Here, cells respond to specific signals that instruct them to either grow or kill themselves. If cells ignore these signals their uncontrolled growth can cause cancer. [37] Generally, mathematical models incorporating only mutation and natural selection have been used to model adaptation and evolution. However, incorporation of game theory can aid the generation of reliable models. [127] [128] Cooperation is now seen as a fundamental property needed for evolution to construct new levels of organization. That selfish replicators could sacrifice their own reproductive potential to cooperate seems paradoxical in a competitive world, however a number of mechanisms can generate cooperation, such as kin selection and group selection, as well as direct, indirect and network reciprocity. [129] The ubiquity of cooperation in the natural world reveals that cooperation is a common outcome of evolution. [130] [131]


    For more details on this topic, see Speciation.
    The geographical isolation of Darwin's finches on the Galápagos Islands led to the rise of over a dozen distinct species. Their beak shapes reflect adaptations to many different food sources. The geographical isolation of Darwin's finches on the Galápagos Islands led to the rise of over a dozen distinct species. Their beak shapes reflect adaptations to many different food sources.

    Speciation is the process where a species diverges into two descendant species. [132] These speciation events have been observed multiple times in both plants and animals, under controlled laboratory conditions and in nature. [133] [134] [135] Since the pair of species produced by speciation are equally descended from the ancestral form, it is incorrect to view one daughter species as the "original" and the other the "new" species. However, this mistake is a common misconception about evolution, and gives rise to ideas such that if humans evolved from monkeys, monkeys should no longer exist. However, humans did not evolve from monkeys — instead humans share a common ancestor with monkeys that was neither human nor monkey. [136] [137]

    In sexually reproducing organisms, speciation results from reproductive isolation and then genealogical divergence. There are four mechanisms for speciation. The most common in animals is allopatric speciation, which occurs in populations that initially become isolated geographically, such as by habitat fragmentation or migration. Simply by virtue of being geographically separated, selection and drift will act independently in the isolated populations. If isolation is maintained, the separate evolutionary process will eventually produce reproductive incompatibility. [138]

    In contrast, the second mode, sympatric speciation, is species divergence without geographic isolation, and its identification is typically controversial, since even a small amount of gene flow may be sufficient to homogenize a potentially diverging species. [139] [140] Generally, models of sympatric speciation in animals require the evolution of stable polymorphisms associated with non-random assortative mating, in order for reproductive isolation to evolve. [141] However, a common mechanism of sympatric speciation in plants appears to the the formation of polyploid species and can involve either a single plant doubling its numbers of chromosomes (an autopolyploid such as cabbage), [142] or two related plants cross-breeding to form an allopolyploid such as wheat. [143] [144]

    Comparison of allopatric, peripatric, parapatric and sympatric speciation. alt Comparison of allopatric, peripatric, parapatric and sympatricspeciation.

    The third mechanism of speciation is peripatric speciation, which occurs as a result of small populations of organisms becoming isolated in a new environment. Here, the founder effect causes rapid speciation through both rapid genetic drift and selection on a reduced gene pool. [145] In parapatric speciation there is no specific extrinsic barrier to gene flow. The population is continuous, but nonetheless, the population does not mate randomly. Individuals are more likely to mate with their geographic neighbors than with individuals in a different part of the population’s range. In this mode, divergence may happen because of reduced gene flow within the population and varying selection pressures across the population’s range. Peripatric speciation is commonly cited as contributing to punctuated equilibrium, [146] which describes speciation as proceeding in short "bursts" interspersed with long periods of stasis, where species remain relatively unchanged. [147] Here, the majority of the fossil record will correspond to the parental population, with the isolated organisms rarely being preserved and consequently few intermediate forms being fossilized.

    Finally, the fourth mechanism of speciation is parapatric speciation, which is similar to peripatric speciation, in that a small population enters a new habitat. However, there in this type of speciation there is no physical separation between these two populations. Instead, speciation results from the evolution of biological mechanisms that reduce gene flow between the two populations. [132] Generally, this occurs when there has been a drastic change in the environment within the original species' habitat. An example of this is the grass genus Anthoxanthum odoratum, which can undergo parapatric speciation in response to localized metal pollution from mines. [148] Here, around the mine, there is selection for resistance to high levels of metals in the soil. Selection against interbreeding with the metal-sensitive parental population produces a change in flowering time of the metal-resistant plants resulting in reproductive isolation. Selection against hybrids between the two populations may result in reinforcement, which is the evolution of traits that promote mating within a species, as well as character displacement, which causes two species to become more distinct. [149]


    For more details on this topic, see Extinction.
    A Tarbosaurus skeleton. All non-avian dinosaur species died in a mass extinction. alt A Tarbosaurus skeleton. All non-avian dinosaur species died in a mass extinction.

    Extinction is the disappearance of entire species. Extinction is not an unusual event on a geological time scale as species regularly appear through speciation, and disappear through extinction. [150] Indeed, virtually all animal and plant species that have ever lived on the earth are now extinct. [151] These extinctions have happened continuously throughout the history of life, although the rate of extinction spikes in occasional mass extinction events. [152] The Permian-Triassic extinction event was the Earth's most severe extinction event, rendering extinct 96% of all species. [152] In the later Cretaceous-Tertiary extinction event, 76% of all species perished, the most commonly mentioned among them being the non-avian dinosaurs. [152] The Holocene extinction event is the mass extinction associated with humanity's expansion across the globe over the last few thousand years and involves the rapid extinction of hundreds of thousands of species and the loss of up to 30% of all species by the mid 21st century. [153] Human activities are probably the cause of the ongoing extinction event, [154] and climate change may further accelerate it in the future. [155] [156]

    The role of extinction in evolution depends on which type is considered. The cause of the continuous "low-level" extinction events, which form the majority of known extinctions, are not well understood and may be the result of competition between species for shared resources. [19] This could produce "species selection" as an additional and important level of natural selection. [68] The intermittent mass extinctions are also important, but instead of acting as a selective force they drastically reduce diversity in a non-specific manner and may therefore promote a burst of adaptive radiation in survivors. [152]

    Evolutionary history of life

    Origin of life

    For more details on this topic, see Timeline of evolution.

    Life must exist before it starts diversifying, and so the origin of life (or abiogenesis) is a necessary precursor for biological evolution. [157] However, understanding that evolution has occurred and investigating how this happens does not require an understanding of the origin of life. [158] Nonetheless, abiogenesis is a subject which is often discussed under the general heading of evolution. [157] The current scientific consensus is that life began from self-catalytic chemical reactions, but disputes over what defines life make the point at which such increasingly-complex sets of reactions became organisms unclear. [159] Not much is certain about the earliest developments in life, the structure of the first living things, or the identity of the last universal common ancestor. [160] [161] Consequently, there is no scientific consensus on what would be involved in abiogenesis but discussions generally focus on self-replicating molecules such as RNA, [162] the behavior of complex systems, and the assembly of protocells. [163]

    Common descent

    For more details on this topic, see Evidence of common descent, Common descent, and Homology (biology).
    The hominoids are descendants of a common ancestor. alt The hominoids are descendants of a common ancestor.

    All organisms on Earth are descended from a common ancestor or ancestral gene pool, which originated from the origin of life. The current set of species on earth are the final products of the process of evolution, with their diversity the product of a long series of speciation and extinction events. [164] [165] In the Origin of Species, Darwin inferred the common descent of organisms from four simple facts. [61] Firstly, organisms have geographic distributions that cannot be explained by local ecology or adaptation alone. Secondly, the diversity of life is not a diversity of completely unique organisms, but a diversity of organisms that show morphological similarities with one another. Thirdly, many organisms have vestigial traits that have no clear purpose in their modern bearers and finally, that all of life, as Linneaus and others had described, can be classified using these similarities into a hierarchy of nested groups. This last point in particular is strongly consistent with a shared evolutionary history of all organisms that live today or have ever lived.

    Past species have also left records of their evolutionary history. Fossils, along with the comparative anatomy of present-day organisms, constitute the morphological, or anatomical, record. [166] By comparing the anatomies of both modern and extinct species, paleontologists can infer the lineages of those species. However, this approach is most successful for organisms that had hard body parts, such as shells, bones or teeth. Furthermore, as prokeryotes such as bacteria and archaea share a limited set of common morphologies, comparisons of their fossils do not provide information on their ancestry.

    Other evidence for common descent comes from the biochemical similarities between all living organisms. For example, every living cell uses of the same nucleic acids as its genetic material, and all genetic material encodes the same set of amino acids. [167] The development of molecular genetics has also allowed biologists to study the record of evolution left in organisms' genomes and date when the species diverged through the molecular clock produced by mutations. [168] For example, these DNA sequence comparisons have revealed the close genetic similarity between humans and chimpanzees and shed light on when the common ancestor of these species existed. [169] [170]

    Evolutionary tree illustrating the  divergence of modern species from their common ancestor in the center. The three domains are colored, with bacteria blue, archaea green, and eukaryotes red.  Each domain evolved into smaller divisions, resulting in the modern groups of organisms. alt Evolutionary tree illustrating the divergence of modern species from their common ancestor in the center. [171] The three domains are colored, with bacteria blue, archaea green, and eukaryotes red. Each domain evolved into smaller divisions, resulting in the modern groups of organisms.

    Evolution of life

    Despite the uncertainty on how life began, it is clear that microorganisms were the first organisms to inhabit earth, [172] approximately 3–4 billion years ago. [173] Evolution did not produce rapid changes in morphology, [174] and for about 3 billion years until the Ediacaran period, all organisms were microscopic. [175] Therefore, most of the history of life describes microorganisms and it is only about a billion years ago that simple multicellular plants and animals began to appear in the oceans. [172] [176]

    These multicellular forms of life were the eukaryotes and came from ancient bacteria being engulfed by the ancestors of eukaryotic cells, which allowed endosymbiotic associations between the bacteria and the host cell. [177] [91] The engulfed bacteria then evolved into either mitochondria or hydrogenosomes, structures that are still found in all known eukaryotes. [178] Later on, an independent second engulfment of cyanobacterial-like organisms by some mitochondria-containing eukaryotes led to the formation of chloroplasts in algae and plants. [179] [180]

    Soon after the emergence of the first animals, the Cambrian explosion, a geologically brief period of remarkable biological diversity, originated the majority of body plans, or phyla, seen in modern animals, as well as a number of unique lineages that subsequently became extinct. [181] Various triggers for the Cambrian explosion have been proposed, including the accumulation of oxygen in the atmosphere from photosynthesis. [182] [183] About 500 million years ago (mya), plants and fungi colonized the land, and were soon followed by arthropods and other animals. [184] Amphibians first appeared around 300 mya, followed by early amniotes, then mammals around 200 mya and birds around 100 mya (both from "reptile"-like lineages). The human genus arose around 2 mya, with the earliest anatomically-modern humans developing in Africa 100–200 thousand years ago. [185] [186] However, despite this apparent progression, the smaller forms of life that evolved early in this process continue to be highly successful and dominate the earth, with the majority of species prokaryotes and the majority of animals insects. [187]

    Modern research

    For more details on Current research in evolutionary biology, see Evolutionary biology.

    Scholars in a number of academic disciplines continue to document examples of evolution, contributing to a deeper understanding of its underlying mechanisms. Every subdiscipline within biology both informs and is informed by knowledge of the details of evolution, such as in ecological genetics, human evolution, molecular evolution, and phylogenetics. Areas of mathematics (such as bioinformatics), physics, chemistry, and other fields all make important contributions to current understanding of evolutionary mechanisms. Even disciplines as far removed as geology and sociology play a part, since the process of biological evolution has coincided in time and space with the development of both the Earth and human civilization.

    Evolutionary biology is a subdiscipline of biology concerned with the origin and descent of species, as well as their changes over time. It was originally an interdisciplinary field including scientists from many traditional taxonomically-oriented disciplines. For example, it generally includes scientists who may have a specialist training in particular organisms, such as mammalogy, ornithology, or herpetology, but who use those organisms to answer general questions in evolution. Evolutionary biology as an academic discipline in its own right emerged as a result of the modern evolutionary synthesis in the 1930s and 1940s. It was not until the 1970s and 1980s, however, that a significant number of universities had departments that specifically included the term evolutionary biology in their titles.

    Physical anthropology emerged in the late 19th century as the study of human osteology, and the fossilized skeletal remains of other hominids. At that time, anthropologists debated whether their evidence supported Darwin's claims, because skeletal remains revealed temporal and spatial variation among hominids, but Darwin had not offered an explanation of the specific mechanisms that produce variation. With the recognition of Mendelian genetics and the rise of the modern synthesis, however, evolution became both the fundamental conceptual framework for, and the object of study of, physical anthropologists. In addition to studying skeletal remains, they began to study genetic variation among human populations (population genetics); thus, some physical anthropologists began calling themselves biological anthropologists.

    The capability of evolution through selection to produce biological processes and networks optimized for a particular environment has greatly interested mathematicians, scientists and engineers. There has been some recent success in implementing these ideas for artificial uses, including genetic algorithms, which can find the solution to a multi-dimensional problem more quickly than standard software produced by human intelligent designers, and the use of evolutionary fitness landscapes to optimize the design of a system [188] Evolutionary optimization techniques are particularly useful in situations in which it is easy to determine the quality of a single solution, but hard to go through all possible solutions one by one.

    Social and religious controversies

    This caricature of Charles Darwin as an ape reflects the cultural backlash against evolution and common descent. alt This caricature of Charles Darwin as an ape reflects the cultural backlash against evolution and common descent.

    For more details on this topic, see Social effect of evolutionary theory, Creation-evolution controversy, and Objections to evolution.

    Even before the publication of The Origin of Species, the idea that life had evolved was a source of controversy and similar arguments continue to this day. In general, controversy has centered on the philosophical, social, and religious implications of evolution, not on the science of evolution itself; the proposition that biological evolution occurs through the mechanism of natural selection is completely uncontested within the scientific literature. [189] [190] [191]

    As Darwin recognized early on, perhaps the most controversial aspect of evolutionary thought is its application to human beings. Specifically, many object to the idea that all diversity in life, including human beings, arose through natural processes without supernatural intervention. Although many religions, such as Catholicism, have reconciled their beliefs with evolution through theistic evolution, creationistsobject to evolution as it contradicts their theistic origin beliefs. [192] In some countries — notably the United States — these tensions between scientific and religious teachings have fueled the ongoing creation-evolution controversy, a social and religious conflict especially centering on politics and public education. [193] While other scientific fields such as cosmology [194] and earth science [195] also conflict with literal interpretations of many religious texts, evolutionary biology has borne the brunt of these debates.

    Evolution has been used to support philosophical and ethical views that most contemporary scientists consider to have been neither mandated by evolution nor supported by data. [196] For example, the eugenic ideas of Francis Galton were developed into arguments that the human gene pool should be improved by selective breeding policies, including incentives for reproduction for those of "good stock" and the compulsory sterilization, prenatal testing, birth control, and even killing, of those of "bad stock". [197] Another example of an extension of evolutionary theory that is now widely regarded as unwarranted is "Social Darwinism", a term given to the 19th century WhigMalthusian theory developed by Herbert Spencer into ideas about "survival of the fittest" in commerce and human societies as a whole, and by others into claims that social inequality, racism, and imperialism were justified. [198]


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    Further reading

    Introductory reading

    • Jones, S., Darwin's Ghost: The Origin of Species Updated (Ballantine Books, 2001) ISBN 0-345-42277-5
    • Dawkins, R., The Selfish Gene. (Oxford University Press, USA; 3rd edition, 2006) ISBN 0-199-29114-4
    • Gould, SJ, Wonderful Life: The Burgess Shale and the Nature of History. (W. W. Norton & Company, 1990) ISBN 0-393-30700-X
    • Carroll, SB., Endless Forms Most Beautiful: The New Science of Evo Devo and the Making of the Animal Kingdom. (W. W. Norton & Company, 2005) ISBN 0-393-06016-0

    History of evolutionary thought

    • Larson, EJ., Evolution: The Remarkable History of a Scientific Theory. (Modern Library, 2004) ISBN 0-679-64288-9
    • Zimmer, C., Evolution: The Triumph of an Idea. (Academic Internet Publishers, 2006) ISBN 0-060-19906-7

    Advanced reading

    • Williams, GC., Adaptation and Natural Selection: A Critique of some Current Evolutionary Thought. (Princeton University Press, 1966) ISBN 0-691-02357-3
    • Futuyma, DJ., Evolution (Sinauer Associates, 2005) ISBN 0-878-93187-2
    • Mayr, E., What Evolution Is. (Basic Books, 2002) ISBN 0-465-04426-3
    • Coyne, JA. and Orr, HA., Speciation (Sinauer Associates, 2004) ISBN 0-878-93089-2
    • Smith, JM. and Szathmary, E., The Major Transitions in Evolution (Oxford University Press, 1997) ISBN 0-198-50294-X

    External links

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    General information

    History of evolutionary thought

    vde Basic topics in evolutionary biology [hide]

    Evidence of evolution

    Processes of evolution: adaptation - macroevolution - microevolution - speciation

    Population genetic mechanisms: selection - genetic drift - gene flow - mutation

    Evolutionary developmental biology (Evo-devo) concepts: phenotypic plasticity - canalisation - modularity

    Modes of evolution: anagenesis - catagenesis - cladogenesis

    History: History of evolutionary thought - Charles Darwin - The Origin of Species - modern evolutionary synthesis

    Other subfields: ecological genetics - human evolution - molecular evolution - phylogenetics - systematics

    List of evolutionary biology topics - Timeline of evolution

    Retrieved from "http://en.wikipedia.org/wiki/Evolution"

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    Evidence of common descent

    From Wikipedia, the free encyclopedia

    (Redirected from Evidence of evolution) Jump to: navigation, search While on board HMS Beagle, Charles Darwin collected numerous specimens, many new to science, which supported his later theory of evolution by natural selection.

    The wide range of evidence of evolution provides a wealth of information on the natural processes by which the variety of life on Earth developed.

    Fossils are important for estimating when various lineages developed. As fossilization is an uncommon occurrence, usually requiring hard body parts and death near a site where sediments are being deposited, the fossil record only provides sparse and intermittent information about the evolution of life. Evidence of organisms prior to the development of hard body parts such as shells, bones and teeth is especially scarce, but exists in the form of ancient microfossils, as well as impressions of various soft-bodied organisms.

    Comparison of the genetic sequence of organisms has revealed that organisms that are phylogenetically close have a higher degree of sequence similarity than organisms that are phylogenetically distant. Further evidence for common descent comes from genetic detritus such as pseudogenes, regions of DNA that are orthologous to a gene in a related organism, but are no longer active and appear to be undergoing a steady process of degeneration. Since metabolic processes do not leave fossils, research into the evolution of the basic cellular processes is also done largely by comparison of existing organisms. Many lineages diverged at different stages of development, so it is theoretically possible to determine when certain metabolic processes appeared by comparing the traits of the descendants of a common ancestor.


    [ hide ]

    [edit] Evidence from paleontology

    An insect trapped in amber. An insect trapped in amber.

    When organisms die, they often decompose rapidly or are consumed by scavengers, leaving no permanent evidences of their existence. However, occasionally, some organisms are preserved. The remains or traces of organisms from a past geologic age embedded in rocks by natural processes are called fossils. They are extremely important for understanding the evolutionary history of life on Earth, as they provide direct evidence of evolution and detailed information on the ancestry of organisms. Paleontology is the study of past life based on fossil records and their relations to different geologic time periods.

    For fossilization to take place, the traces and remains of organisms must be quickly buried so that weathering and decomposition do not occur. Skeletal structures or other hard parts of the organisms are the most commonly occurring form of fossilized remains (Paul, 1998), (Behrensmeyer, 1980) and (Martin, 1999). There are also some trace "fossils" showing moulds, cast or imprints of some previous organisms.

    As an animal dies, the organic materials gradually decay, such that the bones become porous. If the animal is subsequently buried in mud, mineral salts will infiltrate into the bones and gradually fill up the pores. The bones will harden into stones and be preserved as fossils. This process is known as petrification. If dead animals are covered by wind-blown sand, and if the sand is subsequently turned into mud by heavy rain or floods, the same process of mineral infiltration may occur. Apart from petrification, the dead bodies of organisms may be well preserved in ice, in hardened resin of coniferous trees (amber), in tar, or in anaerobic, acidicpeat. Fossilization can sometimes be a trace, an impression of a form. Examples include leaves and footprints, the fossils of which are made in layers that then harden.

    [edit] Fossil records

    Main article: Fossil record
    Fossil trilobite. Trilobites were hard-shelled arthropods, related to living horseshoe crabs and spiders, that first appeared in significant numbers around 540 mya, dying out 250 mya. Fossil trilobite. Trilobites were hard-shelled arthropods, related to living horseshoe crabs and spiders, that first appeared in significant numbers around 540 mya, dying out 250 mya.

    It is possible to find out how a particular group of organisms evolved by arranging its fossil records in a chronological sequence. Such a sequence can be determined because fossils are mainly found in sedimentary rock. Sedimentary rock is formed by layers of silt or mud on top of each other; thus, the resulting rock contains a series of horizontal layers, or strata. Each layer contains fossils which are typical for a specific time period during which they were made. The lowest strata contain the oldest rock and the earliest fossils, while the highest strata contain the youngest rock and more recent fossils.

    A succession of animals and plants can also be seen from fossil records. Fossil evidence supports the theory that organisms tend to progressively increase in complexity. By studying the number and complexity of different fossils at different stratigraphic levels, it has been shown that older fossil-bearing rocks contain fewer types of fossilized organisms, and they all have a simpler structure, whereas younger rocks contain a greater variety of fossils, often with increasingly complex structures.

    In the past, geologists could only roughly estimate the ages of various strata and the fossils found. They did so, for instance, by estimating the time for the formation of sedimentary rock layer by layer. Today, by measuring the proportions of radioactive and stable elements in a given rock, the ages of fossils can be more precisely dated by scientists. This technique is known as radiometric dating.

    Throughout the fossil record, many species that appear at an early stratigraphic level disappear at a later level. This is interpreted in evolutionary terms as indicating the times at which species originated and became extinct. Geographical regions and climatic conditions have varied throughout the Earth's history. Since organisms are adapted to particular environments, the constantly changing conditions favoured species which adapted to new environments through the mechanism of natural selection.

    According to fossil records, some modern species of plants and animals are found to be almost identical to the species that lived in ancient geological ages. They are existing species of ancient lineages that have remained morphologically (and probably also physiologically) somewhat unchanged for a very long time. Consequently, they are called "living fossils" by laypeople. Examples of "living fossils" include the tuatara, the nautilus, the horseshoe crab, the coelacanth, the ginkgo, the Wollemi pine, and the metasequoia.

    [edit] Extent of the Fossil Record

    Despite the relative rarity of suitable conditions for fossilization, approximately 250,000 fossil species are known[4]. The number of individual fossils this represents varies greatly from species to species, but many millions of fossils have been recovered: for instance, more than three million fossils from the last Ice Age have been recovered from the La Brea Tar Pits in Los Angeles[5]. Many more fossils are still in the ground, in various geological formations known to contain a high fossil density, allowing estimates of the total fossil content of the formation to be made. An example of this occurs in South Africa's Beaufort Formation (part of the Karoo Supergroup, which covers most of South Africa), which is rich in vertebrate fossils, including therapsids (reptile/mammal transitional forms)[6]. It has been estimated[7] that this formation contains 800 billion vertebrate fossils.

    [edit] Evolution of the horse

    Further information: Evolution of the horse
    Evolution of the horse showing reconstruction of the fossil species obtained from successive rock strata. The foot diagrams are all front views of the left forefoot. The third metacarpal is shaded throughout. The teeth are shown in longitudinal section.

    Due to an almost-complete fossil record found in North American sedimentary deposits from the early Eocene to the present, the horse provides one of the best examples of evolutionary history (phylogeny).

    This evolutionary sequence starts with a small animal called the Hyracotherium which lived in North America about 54 million years ago, then spread across to Europe and Asia. Fossil remains of Hyracotherium show it to have differed from the modern horse in three important respects: it was a small animal (the size of a fox), lightly built and adapted for running; the limbs were short and slender, and the feet elongated so that the digits were almost vertical, with four digits in the forelimbs and three digits in the hindlimbs; and the incisors were small, the molars having low crowns with rounded cusps covered in enamel.

    The probable course of development of horses from Hyracotherium to Equus (the modern horse) involved at least 12 genera and several hundred species. The major trends seen in the development of the horse to changing environmental conditions may be summarized as follows:

    • Increase in size (from 0.4 m to 1.5 m);
    • Lengthening of limbs and feet;
    • Reduction of lateral digits;
    • Increase in length and thickness of the third digit;
    • Increase in width of incisors;
    • Replacement of premolars by molars; and
    • Increases in tooth length, crown height of molars.

    Fossilized plants found in different strata show that the marshy, wooded country in which Hyracotherium lived became gradually drier. Survival now depended on the head being in an elevated position for gaining a good view of the surrounding countryside, and on a high turn of speed for escape from predators, hence the increase in size and the replacement of the splayed-out foot by the hoofed foot. The drier, harder ground would make the original splayed-out foot unnecessary for support. The changes in the teeth can be explained by assuming that the diet changed from soft vegetation to grass. A dominant genus from each geological period has been selected to show the progressive development of the horse. However, it is important to note that there is no evidence that the forms illustrated are direct descendants of each other, even though they are related.

    [edit] Limitations

    The fossil record is an important source for scientists when tracing the evolutionary history of organisms. However, because of limitations inherent in the record, there are not fine scales of intermediate forms between related groups of species. This lack of continuous fossils in the record is a major limitation in tracing the descent of biological groups. Furthermore, there are also much larger gaps between major evolutionary lineages. These gaps are often referred to as "missing links".

    There is a gap of about 100 million years between the early Cambrian period and the later Ordovician period. The early Cambrian period was the period from which numerous fossils of sponges, cnidarians (e.g., jellyfish), echinoderms (e.g., eocrinoids), molluscs (e.g., snails) and arthropods (e.g., trilobites) are found. In the later Ordovician period, the first animal that really possessed the typical features of vertebrates, the Australianfish, Arandaspis appeared. Thus few, if any, fossils of an intermediate type between invertebrates and vertebrates have been found, although likely candidates include the Burgess Shale animal, Pikaia gracilens, and its Maotianshan Shales relatives, Myllokunmingia, Yunnanozoon, Haikouella lanceolata, and Haikouichthys.

    Some of the reasons for the incompleteness of fossil records are:

    • In general, the probability that an organism becomes fossilized after death is very low;
    • Some species or groups are less likely to become fossils because they are soft-bodied;
    • Some species or groups are less likely to become fossils because they live (and die) in conditions that are not favourable for fossilization to occur in;
    • Many fossils have been destroyed through erosion and tectonic movements;
    • Some fossil remains are complete, but most are fragmentary;
    • Some evolutionary change occurs in populations at the limits of a species' ecological range, and as these populations are likely to be small, the probability of fossilization is lower (see punctuated equilibrium);
    • Similarly, when environmental conditions change, the population of a species is likely to be greatly reduced, such that any evolutionary change induced by these new conditions is less likely to be fossilized;
    • Most fossils convey information about external form, but little about how the organism functioned;
    • Using present-day biodiversity as a guide, this suggests that the fossils unearthed represent only a small fraction of the large number of species of organisms that lived in the past.

    [edit] Evidence from comparative anatomy

    Comparative study of the anatomy of groups of animals or plants reveals that certain structural features are basically similar. For example, the basic structure of all flowers consists of sepals, petals, stigma, style and ovary; yet the size, colour, number of parts and specific structure are different for each individual species.

    [edit] Homologous structures and divergent (adaptive) evolution

    If widely separated groups of organisms are originated from a common ancestry, they are expected to have certain basic features in common. The degree of resemblance between two organisms should indicate how closely related they are in evolution:

    • Groups with little in common are assumed to have diverged from a common ancestor much earlier in geological history than groups which have a lot in common;
    • In deciding how closely related two animals are, a comparative anatomist looks for structures that are fundamentally similar, even though they may serve different functions in the adult. Such structures are described as homologous and suggest a common origin.
    • In cases where the similar structures serve different functions in adults, it may be necessary to trace their origin and embryonic development. A similar developmental origin suggests they are the same structure, and thus likely to be derived from a common ancestor.

    When a group of organisms share a homologous structure which is specialized to perform a variety of functions in order to adapt different environmental conditions and modes of life are called adaptive radiation. The gradual spreading of organisms with adaptive radiation is known as divergent evolution.

    [edit] Pentadactyl limb

    Figure 5a: The principle of homology illustrated by the adaptive radiation of the forelimb of mammals. All conform to the basic pentadactyl pattern but are modified for different usages. The third metacarpal is shaded throughout; the shoulder is crossed-hatched.

    The pattern of limb bones called pentadactyl limb is an example of homologous structures (Fig. 5a). It is found in all classes of tetrapods (i.e. from amphibians to mammals). It can even be traced back to the fins of certain fossil fishes from which the first amphibians are thought to have evolved. The limb has a single proximal bone (humerus), two distal bones (radius and ulna), a series of carpals (wrist bones), followed by five series of metacarpals (palm bones) and phalanges (digits). Throughout the tetrapods, the fundamental structures of pentadactyl limbs are the same, indicating that they originated from a common ancestor. But in the course of evolution, these fundamental structures have been modified. They have become superficially different and unrelated structures to serve different functions in adaptation to different environments and modes of life. This phenomenon is clearly shown in the forelimbs of mammals. For example:

    • In the monkey, the forelimbs are much elongated to form a grasping hand for climbing and swinging among trees.
    • In the pig, the first digit is lost, and the second and fifth digits are reduced. The remaining two digits are longer and stouter than the rest and bear a hoof for supporting the body.
    • In the horse, the forelimbs are adapted for support and running by great elongation of the third digit bearing a hoof.
    • The mole has a pair of short, spade-like forelimbs for burrowing.
    • The anteater uses its enlarged third digit for tearing down ant hills and termite nests.
    • In the whale, the forelimbs become flippers for steering and maintaining equilibrium during swimming.
    • In the bat, the forelimbs have turned into wings for flying by great elongation of four digits, and the hook-like first digit remains free for hanging from trees.

    [edit] Insect mouthparts

    Figure 5b: Adaptive radiation of insect mouthparts: a, antennae; c, compound eye; lb, labrium; lr, labrum; md, mandibles; mx, maxillae.

    The basic structures are the same which include a labrum (upper lip), a pair of mandibles, a hypopharynx (floor of mouth), a pair of maxillae and a labium. These structures are enlarged and modified; others are reduced and lost. The modifications enable the insects to exploit a variety of food materials (Fig. 5b):

    (A) Primitive state — biting and chewing: e.g.grasshopper. Strong mandibles and maxillae for manipulating food.

    (B) Ticking and biting: e.g.honey bee. Labium long to lap up nectar; mandibles chew pollen and mould wax.

    (C) Sucking: e.g.butterfly. Labrum reduced; mandibles lost; maxillae long forming sucking tube.

    (D) Piercing and sucking, e.g. female mosquito. Labrum and maxillae form tube; mandibles form piercing stylets; labrum grooved to hold other parts.

    [edit] Other Arthropod Appendages

    Insect mouthparts and antennae are considered homologues of insect legs. Parallel developments are seen in some arachnids: The anterior pair of legs may be modified as analogues of antennae, particularly in whip scorpians, which walk on six legs. These developments provide support for the theory that complex modifications often arise by duplication of components, with the duplicates modified in different directions.

    [edit] Analogous structures and convergent evolution

    Figure 6: Inverted retina of vertebrate (left) and non-inverted retina of octopus (right)

    Under similar environmental conditions, fundamentally different structures in different groups of organisms may undergo modifications to serve similar functions. This phenomenon is called convergent evolution. Similar structures, physiological processes or mode of life in organisms apparently bearing no close phylogenetic links but showing adaptations to perform the same functions are described as analogous, for example:

    • Wings of bats, birds and insects;
    • the jointed legs of insects and vertebrates;
    • tail fin of fish, whale and lobster;
    • eyes of the vertebrates and cephalopod molluscs (squid and octopus). Fig. 6 illustrates difference between an inverted and non-inverted retina, the sensory cells lying beneath the nerve fibres. This results in the sensory cells being absent where the optic nerve is attached to the eye, thus creating a blind spot. The octopus eye has a non-inverted retina in which the sensory cells lie above the nerve fibres. There is therefore no blind spot in this kind of eye. Apart from this difference the two eyes are remarkably similar, an example of convergent evolution.
    See also: Evolution of the eye

    [edit] Vestigial organs

    Main article: Vestigial structure

    A further aspect of comparative anatomy is the presence of vestigial organs. Organs that are smaller and simpler in structure than corresponding parts in the ancestral species are called vestigial organs. They are usually degenerated or underdeveloped. The existence of vestigial organs can be explained in terms of changes in the environment or modes of life of the species. Those organs are thought to be functional in the ancestral species but have now become unnecessary and non-functional. Examples are the vestigial hind limbs of whales, the haltere (vestigial hind wings) of flies and mosquitos, vestigial wings of flightless birds such as ostriches, and the vestigial leaves of some xerophytes (e.g.cactus) and parasitic plants (e.g.dodder). It must be noted however, that vestigial structures have lost the original function but may have another one. For example the halteres in dipterists help balance the insect while in flight and the wings of ostriches are used in mating rituals.

    [edit] Evidence from geographical distribution

    Biologists have discovered many puzzling facts about the presence of certain species on various continents and islands (biogeography).

    [edit] Continental distribution

    All organisms are adapted to their environment to a greater or lesser extent. If the abiotic and biotic factors within a habitat are capable of supporting a particular species in one geographic area, then one might assume that the same species would be found in a similar habitat in a similar geographic area, e.g. in Africa and South America. This is not the case. Plant and animal species are discontinuously distributed throughout the world:

    Even greater differences can be found if Australia is taken into consideration though it occupies the same latitude as South America and Africa. Marsupials like the kangaroo can be found in Australia, but are totally absent from Africa and are only represented by the opossum in South America and the Virginia Opossum in North America:

    • The echidna and platypus, the only living representatives of primitive egg-laying mammals (monotremes), can be found only in Australia and are totally absent in the rest of the world.
    • On the other hand, Australia has very few placental mammals except those that have been introduced by human beings.

    [edit] Explanation

    Figure 7: Diagrams to the land bridge between continents in past geological time (A) and the barriers formed (B) due to the submergence of land bridges. Figure 7: Diagrams to the land bridge between continents in past geological time (A) and the barriers formed (B) due to the submergence of land bridges.

    The main groups of modern mammal arose in Northern Hemisphere and subsequently migrated to three major directions:

    • to South America via the land bridge in the Bering Strait and Isthmus of Panama; A large number of families of South American marsupials became extinct as a result of competition with these North American counterparts.
    • to Africa via the Strait of Gibraltar; and
    • to Australia via South East Asia to which it was at one time connected by land

    The shallowness of the Bering Strait would have made the passage of animals between two northern continents a relatively easy matter, and it explains the present-day similarity of the two faunas. But once they had got down into the southern continents, they presumably became isolated from each other by various types of barriers.

    • The submerging of the Isthmus of Panama: isolates the South American fauna
    • the Mediterranean Sea and the North African desert: partially isolate the African fauna; and
    • the submerging of the original connection between Australia and South East Asia: isolates the Australian fauna

    Once isolated, the animals in each continent have shown adaptive radiation (Fig. 7) to evolve along their own lines.

    [edit] Evidence for migration and isolation

    Map of the world showing distribution of present members of camel. Solid black lines indicate possible migration routes. Map of the world showing distribution of present members of camel. Solid black lines indicate possible migration routes.

    The fossil record for the camel indicated that evolution of camels started in North America, from which they migrated across the Bering Strait into Asia and hence to Africa, and through the Isthmus of Panama into South America. Once isolated, they evolved along their own lines, giving the modern camel in Asia and Africa and llama in South America.

    [edit] Continental drift

    The same kinds of fossils are found from areas known to be adjacent to one another in the past but which, through the process of continental drift, are now in widely divergent geographic locations. For example, fossils of the same types of ancient amphibians, arthropods and ferns are found in South America, Africa, India, Australia and Antarctica, which can be dated to the Paleozoic Era, at which time these regions were united as a single landmass called Gondwana. [8] Sometimes the descendants of these organisms can be identified and show unmistakable similarity to each other, even though they now inhabit very different regions and climates.

    [edit] Oceanic island distribution

    Most small isolated islands only have native species that could have arrived by air or water; like birds, insects and turtles. The few large mammals present today were brought by human settlers in boats. Plant life on remote and recent volcanic islands like Hawaii could have arrived as airborne spores or as seeds in the droppings of birds. After the explosion of Krakatoa a century ago and the emergence of a steaming, lifeless remnant island called Anak Krakatoa (child of Krakatoa), plants arrived within months and within a year there were moths and spiders that had arrived by air. The island is now ecologially hard to distinguish from those around it that have been there for millions of years.

    [edit] Evidence from comparative physiology and biochemistry

    See also:Archaeogenetics, Common descent, Last universal ancestor, Most recent common ancestor,Nothing in Biology Makes Sense Except in the Light of Evolution, Speciation, Timeline of evolution, Timeline of human evolution, Universal Code (Biology)

    [edit] Evolution of widely distributed proteins and molecules

    All known extant organisms make use of DNA and/or RNA. ATP is used as metabolic currency by all extant life. The Genetic code is the same for almost every organism, meaning that a piece of RNA in a bacterium codes for the same protein as in a human cell.

    A classic example of biochemical evidence for evolution is the variance of the proteinCytochrome c in living cells. The variance of cytochrome c of different organisms is measured in the number of differing amino acids, each differing amino acid being a result of a base pair substitution, a mutation. If each differing amino acid is assumed to be the result of one base pair substitution, it can be calculated how long ago the two species diverged by multiplying the number of base pair substitutions by the estimated time it takes for a substituted base pair of the cytochrome c gene to be successfully passed on. For example, if the average time it takes for a base pair of the cytochrome c gene to mutate is N years, the number of amino acids making up the cytochrome c protein in monkeys differ by one from that of humans, this leads to the conclusion that the two species diverged N years ago.

    Comparison of the DNA sequences allows organisms to be grouped by sequence similarity, and the resulting phylogenetic trees are typically congruent with traditional taxonomy, and are often used to strengthen or correct taxonomic classifications. Sequence comparison is considered a measure robust enough to be used to correct erroneous assumptions in the phylogenetic tree in instances where other evidence is scarce. For example, neutral human DNA sequences are approximately 1.2% divergent (based on substitutions) from those of their nearest genetic relative, the chimpanzee, 1.6% from gorillas, and 6.6% from baboons. [1] Genetic sequence evidence thus allows inference and quantification of genetic relatedness between humans and other apes. [2] [3] The sequence of the 16S rRNA gene, a vital gene encoding a part of the ribosome, was used to find the broad phylogenetic relationships between all extant life. The analysis, originally done by Carl Woese, resulted in the three-domain system, arguing for two major splits in the early evolution of life. The first split led to modern Bacteria and the subsequent split led to modern Archaea and Eukaryote.

    The proteomic evidence also supports the universal ancestry of life. Vital proteins, such as the ribosome, DNA polymerase, and RNA polymerase, are found in everything from the most primitive bacteria to the most complex mammals. The core part of the protein is conserved across all lineages of life, serving similar functions. Higher organisms have evolved additional protein subunits, largely affecting the regulation and protein-protein interaction of the core. Other overarching similarities between all lineages of extant organisms, such as DNA, RNA, amino acids, and the lipid bilayer, give support to the theory of common descent. The chirality of DNA, RNA, and amino acids is conserved across all known life. As there is no functional advantage to right- or left-handed molecular chirality, the simplest hypothesis is that the choice was made randomly by early organisms and passed on to all extant life through common descent. Further evidence for reconstructing ancestral lineages comes from junk DNA such as pseudogenes, "dead" genes which steadily accumulate mutations. [4]

    There is also a large body of molecular evidence for a number of different mechanisms for large evolutionary changes, among them: genome and gene duplication, which facilitates rapid evolution by providing substantial quantities of genetic material under weak or no selective constraints; horizontal gene transfer, the process of transferring genetic material to another cell that is not an organism's offspring, allowing for species to acquire beneficial genes from each other; and recombination, capable of reassorting large numbers of different alleles and of establishing reproductive isolation. The Endosymbiotic theory explains the origin of mitochondria and plastids (e.g.chloroplasts), which are organelles of eukaryotic cells, as the incorporation of an ancient prokaryotic cell into ancient eukaryotic cell. Rather than evolving eukaryoticorganelles slowly, this theory offers a mechanism for a sudden evolutionary leap by incorporating the genetic material and biochemical composition of a separate species. Evidence supporting this mechanism has recently been found in the protistHatena: as a predator it engufes a green algae cell, which subsequently behaves as an endosymbiont, nourishing Hatena, which in turn loses it's feeding apparatus and behaves as an autotroph. [5] [6]

    Since metabolic processes do not leave fossils, research into the evolution of the basic cellular processes is done largely by comparison of existing organisms. Many lineages diverged when new metabolic processes appeared, and it is theoretically possible to determine when certain metabolic processes appeared by comparing the traits of the descendants of a common ancestor or by detecting their physical manifestations. As an example, the appearance of oxygen in the earth's atmosphere is linked to the evolution of photosynthesis.

    [edit] Out of Africa hypothesis of human evolution

    Mathematical models of evolution, pioneered by the likes of Sewall Wright, Ronald Fisher and J. B. S. Haldane and extended via diffusion theory by Motoo Kimura, allow predictions about the genetic structure of evolving populations. Direct examination of the genetic structure of modern populations via DNA sequencing has recently allowed verification of many of these predictions. For example, the Out of Africa theory of human origins, which states that modern humans developed in Africa and a small sub-population migrated out (undergoing a population bottleneck), implies that modern populations should show the signatures of this migration pattern. Specifically, post-bottleneck populations (Europeans and Asians) should show lower overall genetic diversity and a more uniform distribution of allele frequencies compared to the African population. Both of these predictions are borne out by actual data from a number of studies. [citation needed]

    [edit] External link

    [edit] Evidence from antibiotic and pesticide resistance

    The development and spread of antibiotic resistantbacteria, like the spread of pesticide resistant forms of plants and insects is evidence for evolution of species, and of change within species. Thus the appearance of vancomycin resistant Staphlococcus aureus, and the danger it poses to hospital patients is a direct result of evolution through natural selection. Similarly the appearance of DDT resistance in various forms of Anopheles mosqitoes, and the appearance of myxomatosis resistance in breeding rabbit populations in Australia, are all evidence of the existence of evolution in situations of evolutionary selection pressure in species in which generations occur rapidly.

    [edit] Evidence from studies of complex iteration

    "It has taken more than five decades, but the electronic computer is now powerful enough to simulate evolution" [9] assisting bioinformatics in its attempt to solve biological problems.

    Computer science allows the iteration of self changing complex systems to be studied, allowing a mathematically exact understanding of the nature of the processes behind evolution; providing evidence for the hidden causes of known evolutionary events. The evolution of specific cellular mechanisms like spliceosomes that can turn the cell's genome into a vast workshop of billions of interchangeable parts that can create tools that create tools that create tools that create us can be studied for the first time in an exact way.

    For example, Christoph Adami et al. make this point in Evolution of biological complexity:

    To make a case for or against a trend in the evolution of complexity in biological evolution, complexity needs to be both rigorously defined and measurable. A recent information-theoretic (but intuitively evident) definition identifies genomic complexity with the amount of information a sequence stores about its environment. We investigate the evolution of genomic complexity in populations of digital organisms and monitor in detail the evolutionary transitions that increase complexity. We show that, because natural selection forces genomes to behave as a natural "Maxwell Demon," within a fixed environment, genomic complexity is forced to increase. [10]

    For example, David J. Earl and Michael W. Deem make this point in Evolvability is a selectable trait:

    Not only has life evolved, but life has evolved to evolve. That is, correlations within protein structure have evolved, and mechanisms to manipulate these correlations have evolved in tandem. The rates at which the various events within the hierarchy of evolutionary moves occur are not random or arbitrary but are selected by Darwinian evolution. Sensibly, rapid or extreme environmental change leads to selection for greater evolvability. This selection is not forbidden by causality and is strongest on the largest-scale moves within the mutational hierarchy. Many observations within evolutionary biology, heretofore considered evolutionary happenstance or accidents, are explained by selection for evolvability. For example, the vertebrate immune system shows that the variable environment of antigens has provided selective pressure for the use of adaptable codons and low-fidelity polymerases during somatic hypermutation. A similar driving force for biased codon usage as a result of productively high mutation rates is observed in the hemagglutinin protein of influenza A. [11]

    "Computer simulations of the evolution of linear sequences have demonstrated the importance of recombination of blocks of sequence rather than point mutagenesis alone. Repeated cycles of point mutagenesis, recombination, and selection should allow in vitro molecular evolution of complex sequences, such as proteins." [12] Evolutionary molecular engineering, also called directed evolution or in vitro molecular evolution involves the iterated cycle of mutation, multiplication with recombination, and selection of the fittest of individual molecules (proteins, DNA, and RNA). Natural evolution can be relived showing us possible paths from catalytic cycles based on proteins to based on RNA to based on DNA. [13][14][15][16]

    [edit] Evidence from speciation

    [edit] Hawthorn fly

    An interesting example of evolution at work is the case of the hawthorn fly, Rhagoletis pomonella, which appears to be undergoing sympatric speciation. [7] Different populations of hawthorn fly feed on different fruits. A distinct population emerged in North America in the 19th century some time after apples, a non-native species, were introduced. This apple-feeding population normally feeds only on apples and not on the historically preferred fruit of hawthorns. The current hawthorn feeding population does not normally feed on apples. Some evidence, such as the fact that six out of thirteen allozyme loci are different, that hawthorn flies mature later in the season and take longer to mature than apple flies; and that there is little evidence of interbreeding (researchers have documented a 4-6% hybridization rate) suggests that this is occurring. The emergence of the new hawthorn fly is an example of evolution in progress. [8]

    [edit] References

    1. ^ Two sources: 'Genomic divergences between humans and other hominoids and the effective population size of the common ancestor of humans and chimpanzees'. and 'Quantitative Estimates of Sequence Divergence for Comparative Analyses of Mammalian Genomes' "[1][2]"
    2. ^ The picture labeled "Human Chromosome 2 and its analogs in the apes" in the article Comparison of the Human and Great Ape Chromosomes as Evidence for Common Ancestry is literally a picture of a link in humans that links two separate chromosomes in the nonhuman apes creating a single chromosome in humans. It is considered a missing link, and the ape-human connection is of particular interest. Also, while the term originally referred to fossil evidence, this too is a trace from the past corresponding to some living beings which when alive were the physical embodiment of this link.
    3. ^ The New York Times report Still Evolving, Human Genes Tell New Story, based on A Map of Recent Positive Selection in the Human Genome, states the International HapMap Project is "providing the strongest evidence yet that humans are still evolving" and details some of that evidence.
    4. ^ Pseudogene evolution and natural selection for a compact genome. "[3]"
    5. ^ Okamoto N, Inouye I. (2005). "A secondary symbiosis in progress". Science310 (5746): 287.
    6. ^ Okamoto N, Inouye I. (2006). "Hatena arenicola gen. et sp. nov., a Katablepharid Undergoing Probable Plastid Acquisition.". ProtistArticle in Print.
    7. ^ Feder et al (2003). "Evidence for inversion polymorphism related to sympatric host race formation in the apple maggot fly, Rhagoletis pomonella.". Genetics163 (3): 939-953.
    8. ^ Berlocher, S.H. and G.L. Bush. 1982. An electrophoretic analysis of Rhagoletis (Diptera: Tephritidae) phylogeny. Systematic Zoology 31:136-155; Berlocher, S.H. and J.L. Feder. 2002. Sympatric speciation in phytophagous insects: moving beyond controversy? Annual Review of Entomology 47:773-815; Bush, G.L. 1969. Sympatric host race formation and speciation in frugivorous flies of the genus Rhagoletis (Diptera: Tephritidae). Evolution 23:237-251; Prokopy, R.J., S.R. Diehl and S.S. Cooley. 1988. Behavioral evidence for host races in Rhagoletis pomonella flies. Oecologia 76:138-147. Proc. Natl. Acad. Sci. USA - Vol. 94, pp. 11417-11421, October 1997 - Evolution article Selective maintenance of allozyme differences among sympatric host races of the apple maggot fly.
    • Darwin, Charles November 24, 1859. On the Origin of Species by means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life. London: John Murray, Albemarle Street. 502 pages. Reprinted: Gramercy (May 22, 1995). ISBN 0-517-12320-7
    • Mayr, Ernst. What Evolution Is. Basic Books (October, 2002). ISBN 0-465-04426-3
    • Gigerenzer, Gerd, et al., The empire of chance: how probability changed science and everyday life (New York: Cambridge University Press, 1989).
    • Williams, G.C. (1966). Adaptation and Natural Selection: A Critique of some Current Evolutionary Thought. Princeton, N.J.: Princeton University Press.
    • Biological science, Oxford, 2002.
    • CJ Clegg, 1999, Genetics and Evolution, John Murray. ISBN 0-7195-7552-4
    • Y.K. Ho, 2004, Advanced-level Biology for Hong Kong, Manhattan Press. ISBN 962-990-635-X
    • Paul, Christopher R. C. (1998) The Adequacy of the Fossil Record, John Wiley & Sons, ISBN 0-471-96988-5
    • Behrensmeyer, Anna K. (1980) Fossils in the making: Vertebrate taphonomy and paleoecology, University of Chicago Press, ISBN 0-226-04169-7
    • Martin, Ronald E. et al. eds. (1999) Taphonomy: A Process Approach, Cambridge University Press, ISBN 0-521-59833-8

    [edit] External links

    vde Basic topics in evolutionary biology [hide]

    Evidence of evolution

    Processes of evolution: adaptation - macroevolution - microevolution - speciation

    Population genetic mechanisms: selection - genetic drift - gene flow - mutation

    Evolutionary developmental biology (Evo-devo) concepts: phenotypic plasticity - canalisation - modularity

    Modes of evolution: anagenesis - catagenesis - cladogenesis

    History: History of evolutionary thought - Charles Darwin - The Origin of Species - modern evolutionary synthesis

    Other subfields: ecological genetics - human evolution - molecular evolution - phylogenetics - systematics

    List of evolutionary biology topics - Timeline of evolution

  • Arthur

    Hey 5go

    Very interesting reading. Thanks for posting all of this material.

  • 5go

    I have kept my end of the deal now I need my answer and picture.

  • neverendingjourney


    I'm new to this board, and I don't have much of a background in science, so I'll stay out of this one. But, I must ask: Why do you demand that people prove evolution? Do you feel your religious beliefs (I'm assuming you're a religious person) threatened by evolutionary science? I'm something of an Agnostic ever since I left the org., but I don't feel threatened at all by religious persons. Everyone is entitled to their own personal beliefs. I don't go around making demands that they prove the existence of God or any such thing.

    It seems to me that your intent is to start an argument. I realize that many people on both sides of the creation/evolution debate love to argue and attempt to "win" this kind of an argument. However, I spent 10 years in the org. trying to prove that other people's beliefs were wrong and that mine were right. After a while I began to feel sick to my stomach to think that I had the nerve to claim that I had somehow figured out the deep mysteries of life when the brightest minds in history had failed. I left dogmatism behind when I left the org, and I'm much better off for it.

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